i have a nine month old chihuahua and lately he has begun to pee on my bed and on the couch?

It sounds like a territorial thing. He thinks he rules the roost. First of all, if you haven't already, have him neutered. He should have had this at around 6 months of age. That often helps alleviate the problem a little. Secondly, I highly recommend watching "The Dog Whisperer" and learn how you can show him that you're in charge of the house, not him (I say this because the techniques taught in the show are nothing I can accurately describe in writing). Dogs are pack animals and they need a leader to rule the pack (in this case, your household), and if the owner does not take up this role, the dog will. This is why he marks — in his mind, your house = his territory. He needs to learn that it's YOUR couch, YOUR bed, and he isn't allowed to mark it because it's not his. Once you've established leadership correctly, and he respects you as his pack leader, the problem should stop altogether.

Does he also growl, bark, pull at his leash or walk in front of you when you go for walkies? That's all dominant behaviour. It's easier to stop this when they're as young as your puppy is, because he's had little time to settle into his "leadership" role. Chihuahuas can often become aggressive dogs if you let this behaviour continue, so you need to nip it in the bud before it gets worse.

Take him to the vet to be sure he doesn't have a bladder/urinary tract issue. If he doesn't, it's a head thing. Good luck with that one.